1. Evolution and Classification

1.1 Origin of Life and Plants

1.2 Animal Evolution

1.3 Human Evolution

1.4 Mechanisms of Evolution

1.5 Hardy-Weinberg Equilibrium

1.6 Mechanisms of Speciation

1.7 Classification of Living Organisms

1.1 Origin of Life and Plants

What is evolution?

Earliest forms of life began 4 billion years ago. The earths atmosphere was very different: composed of water, methane, ammonia, hydrogen sulfide, carbon dioxide, carbon monoxide, and phosphate – reducing conditions!

A. J. Oparin The earths reducing atmosphere combined with the earth’s cooling and lightning storms resulted in hot seas (primordial soup) where organic molecules (like amino acids) could be formed

S. Miller and H. Urey Mimicked the earths early atmosphere in experiments where small inorganic molecules were exposed to electric charges and created organic building blocks of life, including amino acids

S. Fox Experiments where amino acids formed dipeptides with ultra violet radiation, and under dry heat, polypeptides that contained up to 18 amino acids

C. Ponnamperuma Showed the formation of adenine and ribose from treating gases similar to those found in earth’s early atmosphere with an electric current

With no O2 present in earth’s early atmosphere, the earliest cells were anaerobic.

Some evolved the ability to make their own energy (autotrophs) introducing O2 into the atmosphere

By producing oxygen as a byproduct of photosynthesis, cyanobacteria are thought to have converted the early oxygen-poor, reducing atmosphere, into an oxidizing one

O2 is normally poisonous to anaerobic cells, but some evolved to not only survive oxygen, but incorporate it into their metabolic pathways (aerobic).

These cells incorporated autotrophs and together they evolved into photosynthetic eukaryotic cells.

The earliest plants were probably aquatic, but over time, as niches began to fill in both salt and freshwater areas, plants evolved anatomical adaptations, like cell walls, to allow for life on land.

1.2 Animal Evolution

Animals are thought to have evolved from marine protists – single-celled living organisms. Animal cells are most similar to protist cells, though the fossil record does not go back that far.

The first evidence of multicellular organisms with armor-like exoskeletons

Cambrian Explosion ca. 530 Ma

Diversification of species that survived mass extinction, the emergence of plants growing on land, and the first record of vertebrates (early fish)

Ordovician Period ca. 500 Ma

Land colonization by both plants and animals, which came with new adaptations (gas exchange, skeletons, circulatory system) to survive

Silurian Period ca. 435 Ma

The end of the Paleozoic Era was punctuated by a number of mass extinction events (nearly 95% of developed species)

1.3 Human Evolution

Humans are believed to have evolved from primates that evolved or developed larger brains over time

Earliest humanoid fossils found in the 1970s – Australopithecus afarensis, aka “Lucy”

Earliest human fossils are thought to be 1.8 million years old -Homo erectus

Homology: The existence of structures in two different species that share a common ancestry

Analogy:

The existence of structures in two different species that share a common function but not a common ancestry

Analogous structures are an example of convergent evolution, more than 1 species evolves to fill a niche

1.4 Mechanisms of Evolution

Darwinian vs. Modern understanding of evolution

Darwin focused on natural selection that happened to individuals, modern theory focuses on changes that happen among populations w/in communities

Charles Darwin

Natural Selection: some individuals within a population are better suited for survival under given environmental conditions

Differential Reproduction: those individuals better suited for survival are also more likely to successfully reproduce This strengthens the frequency of expression of “desirable” traits across a population over time

A random alteration or change in a DNA sequence

Sickle cell anemia – a mutation that switches 1 amino acid

Sometimes the mutation leads to a desirable trait (ex. Mutation of CCR5 gene gives some individuals HIV resistance) Sometimes a mutation can lead to an undesirable trait (ex. Mutation of BRCA1 gene can lead to cancer)

Genetic drift impacts the genetic makeup of a population by random chance. Sometimes individuals leave behind a few more offspring than others, and therefore, more genes These genes are then expressed in following generations, even though they are not necessarily the “fittest”

1.5 Hardy-Weinberg Equilibrium

Definition: The frequency of genotype ratios remains constant from one generation to the next in populations at equilibrium with the environment where random mating is occurring

Requirements for Hardy-Weinberg Equilibrium: Random mating, no migration, mutation, selection, or genetic drift can be occurring

The sum of all frequencies of all possible alleles for a single trait is = 1 (or 100%) If p = frequency of allele “A” and q = frequency of allele “B” Then p+q = 1

The frequency of genotypes within a population can be represented mathematically as: p2 + 2pq + q2 =1

p2 is the homozygous dominant genotype q2 is the homozygous recessive genotype and 2pq is the heterozygous genotype

An example: phenylthiocarbamide (PTC) Found in cabbage and broccoli, can give a “bitter” taste, but only for some people (considered a dominant trait)

NH

S

NH2

T = allele for tasting PTC t = allele for non-tasting of PTC Possible genotypes are: TT, Tt, and tt (TT and Tt can taste PTC, and tt can not) Using our equations (p + q = 1) and (p2 + 2pq + q2 =1), if we know p or q, we can solve for the other!

Question: If the frequency of PTC non-tasters (tt) in a population is 4% (or 0.04), (1) solve for the frequency of the allele for tasting PTC, as well as (2) the frequency of the three possible genotypes (TT, Tt, tt).

Part 1) given: tt = 0.04 If tt = q2 = 0.04, solving for q q = the square root of 0.04, or 0.2 (or 20%). We know that p + q = 1, so solving for p, we get p + 0.2 = 1, p = 0.8 (or 80%)

(2) Solve for the frequency of the three possible genotypes (TT, Tt, tt). Plugging in our values to (p2 + 2pq + q2 = 1) (0.8)2 + 2(0.8)(0.2) + (0.2)2 =1 we can then solve

TT = 0.64, or 64% Tt = 0.32, or 32% And tt = 0.04 (or 4%) was given at the beginning

1.6 Mechanisms of Speciation

What is a “species”? How are different species produced?

Allopatric speciation Two geographically isolated populations experience genetic drift and mutations over time, eventually to the point where they can no longer interbreed successfully

Allopatric means “other homeland”

Sympatric speciation Two non-geographically isolated populations emerge from one due to the development of genetic differences where they can no longer interbreed successfully

Sympatric means “same homeland”

Adaptive Radiation Organisms diversify rapidly from an ancestral species into new forms, particularly when a change in the environment makes new resources available, creates new challenges, or opens new environmental niches

Punctuated Equilibrium– small population with rapid environmental change

Gradualism – large population in a stable environment

1.7 Classification of Living Organisms

What is taxonomy?

“Arrangement Law”

A way to classify organisms to construct internationally shared classification systems with each organism placed into more and more inclusive groupings.

Carolus Linnaeus and the 7 Level System

Binomial nomenclature – “2 names” • genus and species • Canis lupus • Homo sapiens

Species: Canis lupus

Genus: Canis

Family: Canidae

Order: Carnivora

Class: Mammalia Phylum: Chordata

Kingdom: Animalia

Domain: Eukarya

The Modern Classification System

3 Different Domains • Archaea • Eubacteria • Eukaryotes

Archaea • Prokaryotes • Unique RNA • Extreme ecosystems

Morning Glory pool, Yellowstone National Park

Eubacteria • Prokaryotes • Bacteria

Scanning electron micrograph of E. coli bacteria.

Eukaryotes • Eukaryotic cells • Contains 4

kingdoms: Protista, Fungi, Animalia, and Plantae